Kinshasha - Outgoing Democratic Republic of Congo President Joseph Kabila's ruling coalition won a majority in legislative elections, a coalition official said on Saturday, despite opposition leader Felix Tshisekedi's win in the presidential vote the same day.

The result will undercut Tshisekedi's ability to deliver on campaign promises to make a break with the 18-year Kabila era and fuel suspicion that his victory, announced on Thursday, came through a backroom deal that will preserve Kabila's influence over important ministries and the security forces.

Kabila is due to step down in the coming days in what was meant to be Congo's first democratic transfer of power in 59 years of independence. But he has signalled he intends to remain involved in politics and might run for president in 2023 when term limits no longer apply.

The runner-up in the presidential election, Martin Fayulu, filed a fraud complaint on Saturday with Congo's highest court to challenge the result, a campaign spokeswoman, Eve Bazaiba, told Reuters.

Fayulu says he won in a landslide in the Dec. 30 ballot with more than 60 percent of votes and accuses Tshisekedi of striking a deal with Kabila to be declared the winner.

Tshisekedi's camp denies that there was any deal with Kabila and says meetings it held with the president's representatives after the election were meant solely to ensure a peaceful transfer of power.

The disputed outcome threatens to reawaken violence in the huge and tumultuous central African country where millions have died during civil wars since the 1990s.

In a tweet before filing the complaint, Fayulu wrote that the election commission CENI's results "were invented out of whole cloth. I demand a hand recount of all votes for the three elections (presidential, national legislative and provincial)".

The court has eight days to rule, but Fayulu has already said he does not expect a favourable judgment since the court is made up of Kabila appointees.

Earlier in the day, about 50 Republican Guard soldiers and police officers surrounded Fayulu's residence, sending dozens of his supporters, who had been chanting against Kabila and Tshisekedi, fleeing inside, a Reuters witness said.

Fayulu's supporters have demonstrated in several cities since the results were announced. Protests in the western city of Kikwit on Thursday turned violent, killing at least four demonstrators and two police officers.

LITTLE ROOM FOR MANOEUVRE

The parliamentary majority retained by the handful of parties in Kabila's coalition will curtail Tshisekedi's room for manoeuvre. Under the constitution, the majority enjoys significant powers and the president must appoint his prime minister from its ranks.

The prime minister, in turn, must countersign presidential orders appointing or dismissing military chiefs, judges and heads of state-owned enterprises.

Adam Chalwe, a national secretary for Kabila's PPRD party, the biggest within the FCC coalition, told Reuters that results from the individual races announced by CENI on Saturday morning showed FCC candidates taking more than 300 out of 500 seats in the National Assembly.

Reuters was not immediately able to confirm that independently.

Parties in the FCC coalition accounted for about 350 seats in the previous legislature.

The coalition's presidential candidate, Emmanuel Ramazani Shadary, finished a distant third with 24 percent of the vote. Pre-election polling had shown the FCC lagging behind opposition parties in legislative races.

Jean Jacques Mamba, a spokesman for the Movement for the Liberation of Congo (MLC) party that backs Fayulu and which polls had shown leading the legislative race, said it had won 22 seats, instead of the 40-50 it had expected.

He accused CENI of rigging the vote using electronic voting machines. CENI officials could not be immediately reached for comment. (Additional reporting by Giulia Paravicini; additional reporting and writing by Aaron Ross, Editing by Ros Russell)